The present invention relates to a rotary regenerative air preheater that includes a cylindrical rotor having a series of adjacent sector-shaped compartments that are mounted radially outward from a central rotor post. A rotor housing that surrounds the rotor is provided with spaced ducts for the axial flow of a heating fluid and of a fluid to be heated.
Due to a thermal gradient across the rotor there will be a differential of expansion effecting distortion that opens a gap permitting leakage between the rotor and the rotor housing. Spring biased sealing means that automatically adjust to close this gap and thus preclude leakage are commonly used. While such means may function in a satisfactory manner when first operational, they inherently corrode, collect deposits, and thus become ineffective in the hot environment to which they are subjected.
In designing springs for use in a hot air environment it has been found that the modulus of elasticity and the elastic limit are reduced with the increase of temperature, thereby lowering permissible stress. Therefore the design of springs used is dependent upon maintaining low design stress at elevated temperatures. It has also been found that the allowable stress used in the design of such apparatus may be increased approximately 75 percent by the use of torsion type springs instead of the compression or tension springs commonly used. This makes an arrangement utilizing a torsion bar type of spring extremely desirable, so it becomes the principal object of this invention to provide a radial seal for a rotary regenerative type air preheater that is biased into a sealing relationship by a torsion type spring.
The art contains various references showing radial sealing means that lie between the rotor and a surrounding rotor housing and are adapted to conform to a differential of expansion therebetween. U.S. Pat. No. 2,607,565 of Aug. 19, 1952, and U.S. Pat. No. 2,666,624 of Jan. 19, 1954, show a sealing means that is biased by an arrangement of coil springs, while U.S. Pat. No. 2,650,074 of Aug. 25, 1953, shows still another variation of a spring biased radial seal that utilizes a conventional spring.
In all the arrangements having a conventional coil or leaf spring, the spring action thereof rapidly degenerates whenever the spring is exposed to continuous heat, corrosion, or erosion.